[Round table: Importance of allergens in childhood asthma. Introduction]

Asthma is the most frequent chronic disease in childhood. Its prevalence varies (in Spain between 12 % in coastal regions and 6 % in the Castilian plateau). Asthma represents chronic inflammation of the airways associated with an increase in bronchial reactivity to various stimuli, leading to reduced air flow and subsequent remodeling of the bronchial wall. Asthma usually begins in the first few years of life and 30 % of patients will continue to be asthmatic throughout their lives. The main characteristic associated with the persistence of asthma in adulthood seems to be allergy. Another risk factor is the presence of bronchial hyperreactivity. Wheezing associated with viral infections in childhood shows a favorable outcome when not associated with atopic features. The atopic disposition is caused by the interaction between genetic and distinct environmental factors (allergens), as well as by the various clinical manifestations that favor a mainly Th2 response, with interleukins that lead to the formation of specific IgE, pro-inflammatory cytokines, bronchial hyperreactivity, etc. In most cases, asthma is mainly an allergic process, mediated by an IgE mechanism. Inhalation of allergens is considered the most important cause of the onset of asthma in predisposed children. First the presence of an allergen gives rise to sensitization, with the formation of specific IgE. In a subsequent contact, mediators are released, with inflammatory response of the airways and an increase in bronchial hyperreactivity. If the presence of the allergen is prolonged, inflammation and subsequent healing may lead to irreversible damage to the bronchial wall and permanent deterioration of respiratory function. In children with asthma, the aim is to modify the natural history of the disease and prevent its persistence in adulthood. This involves identifying the allergen or allergens causing the symptoms, confirming the role of these allergens in clinical manifestations through specific challenge tests and, lastly, indicating the treatment be followed.